"Are we 100% certain this will actually be the true, honest-to-god, real 500,000th error since 1876? No, it undoubtedly isn't as there are lots of accounting discrepancies in the 'official' record, especially in the fielding stats. ... For pre-1970's results, fielding records were mostly an afterthought and no effort was made to make sure they balanced at the end of the season. ...

"One other issue that may affect things is that some errors are overturned at a later date."

But, for better or worse, Reyes has been given this "honor." CBSSports.com has video of the historic moment. He bobbles an infield hit and never does get the throw away. And there's a clip of it at MLB.com as well.